Reduced glutathione, most commonly called glutathione or GSH, is a relatively small molecule found in animals and plants, having the following formula:
Glutathione is a water-phase orthomolecule. It is the smallest intracellular thiol molecule. It is a potent reducing compound due to its significant electron-donating capacity. Glutathione is a potent antioxidant and enzyme cofactor which plays a critical role in regulating cell activity.
Glutathione is a linear tripeptide of L-glutamine, L-cysteine, and glycine. Technically, N-L-gamma-glutamyl-cysteinyl glycine or L-glutathione, the molecule has a sulfhydryl (SH) group on the cysteinyl portion, which accounts for its strong electron-donating character. As electrons are lost, the molecule becomes oxidized, and two oxidized glutathione molecules become linked (dimerized) by a disulfide bridge to form glutathione disulfide or oxidized glutathione (GSSG). This linkage is reversible upon re-reduction. Glutathione is under tight homeostatic control both intracellularly and extracellularly. A dynamic balance is maintained between glutathione synthesis, its recycling from GSSG/oxidized glutathione, and its utilization.
Glutathione synthesis involves two closely linked, enzymatically controlled reactions that utilize ATP. First cysteine and glutamate are combined by gamma-glutamyl cysteinyl synthetase. Second, glutathione synthetase combines gamma-glutamylcysteine with glycine to generate glutathione. As glutathione levels rise, they self-limit further glutathione synthesis; otherwise, cysteine availability is usually rate-limiting. Fasting, protein-energy malnutrition, or other dietary amino acid deficiencies limit glutathione synthesis.
Glutathione recycling is catalyzed by glutathione disulfide reductase, which uses reducing equivalents from NADPH to reconvert GSSG to 2GSH. The reducing power of ascorbate helps conserve systemic glutathione. Glutathione is used as a cofactor by (1) multiple peroxidase enzymes, to detoxify peroxides generated from oxygen radical attack on biological molecules; (2) transhydrogenases, to reduce oxidized centers on DNA, proteins, and other biomolecules; and (3) glutathione S-transferases (GST) to conjugate glutathione with endogenous substances (e.g., estrogens) and to exogenous electrophiles (e.g., arene oxides, unsaturated carbonyls, organic halides), and diverse xenobiotics.
Free radical and other oxidative agents can deplete glutathione. The homeostatic glutathione redox cycle attempts to maintain glutathione levels as it is being consumed. Amounts available from foods are limited (less than 150 mg/day), and oxidative depletion can outpace synthesis.
The liver is the largest glutathione reservoir. The parenchymal cells synthesize glutathione for P450 conjugation and numerous other metabolic requirements, then export glutathione as a systemic source of SH/reducing power. Glutathione is carried in the bile to the intestinal luminal compartment. Epithelial tissues of the kidney tubules, intestinal lining, and lung, have substantial P450 activity and modest capacity to export glutathione.
Glutathione equivalents circulate in the blood predominantly as cysteine, the oxidized and more stable form of cysteine. Cells import cysteine from the blood, reconvert it to cysteine (likely using ascorbate as cofactor), and from it synthesize glutathione. Conversely, inside the cell glutathione helps re-reduce oxidized forms of other antioxidants such as ascorbate and alpha-tocopherol.
Glutathione is an extremely important cell protectant. It directly quenches reactive hydroxyl free radicals, other oxygen-centered free radicals, and radical centers on DNA and other biomolecules. Glutathione protects skin, lens, cornea, and retina against radiation damage, and the biochemical foundation of P450 detoxication in the liver, kidneys, lungs, intestinal epithelia, and other organs.
Glutathione is the essential cofactor for many enzymes which require thiol-reducing equivalents, and helps keep redox-sensitive active sites on enzymes in the necessary reduced state. Higher-order thiol cell systems—the metallothioneins, thioredoxins, and other redox regulator proteins—are ultimately regulated by GSH levels and the GSH/GSSG redox ratio.
Glutathione and its metabolites also interface with energetics and neurotransmitter syntheses, through several prominent metabolic pathways. Glutathione availability down-regulates the pro-inflammatory potential of leukotrienes and other eicosanoids.
Glutathione levels in human tissues normally range from 0.1 to 10 millimolar (mM), most concentrated in the liver (up to 10 mM) and in the spleen, kidney, lens, erythrocytes, and leukocytes. Plasma concentration is in the micromolar range (approx. 4.5 μM). Oxidative stressors that can deplete glutathione include ultraviolet and other radiation; viral infections; environmental toxins, household chemicals, and heavy metals; surgery, inflammation, burns, septic shock; and dietary deficiencies of glutathione precursors and enzyme cofactors.
A number of disclosures teach enhancing the cellular level of glutathione through administration of various glutathione derivatives. U.S. Pat. No. 5,464,825 (Anderson) discloses use of N-acyl monoalkyl glutathione monoester for increasing cellular levels in the liver and kidney cells to treat AIDS and other viral infections. U.S. Pat. No. 5,624,955 (Nagasawa) discloses glutathione prodrugs consisting of glutamyl cysteine derivatives to enhance glutathione level in the lens and prevent cataract onset. U.S. Pat. No. 7,029,695 (Redelmeier) discloses lipid formulations to enhance the bioavailability of analogs of glutathione for use in hematopoiesis modulation. Neuroscience 138:1161-1170 (2006) (Perluigi et al.) discloses use of Tricyclodecan-9-yl-xanthogenate to achieve an increase in glutathione levels in the neuronal cells to treat Alzheimer's disease WO 2009/047728 (Liguri) discloses that lipophilic derivatives of glutathione may be useful in treating Alzheimer disease and Huntington chorea.
Topical uses of glutathione derivatives have been disclosed. U.S. Pat. No. 3,984,569 (Kalopissis) discloses use of S-substituted linear and branched alkyl and alkenyl derivatives of glutathione for various scalp and hair applications and to combat excessive sebum secretion. U.S. Pat. No. 5,516,507 (N'Guyen) discloses glutathione mono-alkyl esters for topical treatment of cutaneous aging. These glutathione mono-alkyl esters are substituted at the glycine residue and employ alkyl chains having only 1 to 10 carbons. U.S. Pat. App. 2004/0147452 (Yu) proposes the use of non-amphoteric N-acyl glutathione derivatives for topical application for a broad range of conditions. The non-amphoteric derivatives of glutathione are proposed due to the instability of aqueous pharmaceutical formulations of mono and diester prodrugs of glutathione, which rapidly deteriorate over time.
U.S. Pat. No. 6,011,067 (Hersh) discloses compositions as adjuncts to topical therapy of desquamating inflammatory disorders, such as psoriasis, which compositions contain as active ingredients L-glutathione and a selenium compound. Hersh's disclosure stresses the importance of the presence of both ingredients to the anti-psoriatic effectiveness of the claimed composition.
My published applications, U.S. Patent Publications Nos. 20050192229, 20060063718; and 20060069036 disclose compositions with high glutathione concentrations for topical use in the treatment of psoriasis.